1. Field of Invention
The present invention relates generally to a robotic locomotor training device.
2. Related Art
In the U.S. alone, over 10,000 people experience a traumatic spinal cord injury each year, and over 200,000 people with spinal cord injury are alive (20). Paralysis of the legs is a common consequence of spinal cord injury, resulting in loss of walking ability. Recently, a new approach to rehabilitation called “body weight supported locomotion training” has shown promise (12, 14, 20, 34, 35, 37, 41, 42, 53, 54, 55, 56). The technique involves suspending a spinal cord injured subject in a harness above a treadmill and manually assisting movement of the legs in a walking pattern. The key characteristics of this technique are partial unloading of the limbs, and assistance of leg movements during stepping on a treadmill. The goal of this technique is to enhance residual locomotor control circuitry that resides in the spinal cord. It is hypothesized that by providing appropriate sensory input (i.e. that associated with the force, position, and touch sensors that remain in the legs) in a repetitive manner, the spinal cord can learn to generate motor output appropriate for stepping.
This new approach to locomotion training is supported by studies of spinal cord injured animals (10, 11, 17, 29, 36, 39, 40, 48, 49, 50, 51, 59). For example, weight supported treadmill training was found to significantly enhance hindlimb stepping ability of spinal cord transected cats, indicating that the lumbar spinal cord can learn to step (8, 14, 22, 23, 37). Based on such animal studies, body weight supported training has been developed as a treatment therapy for humans following spinal cord injury, stroke, and other neurological disorders that impair locomotor ability (18, 19, 21, 25, 26, 27, 31, 56, 57, 58).
Research results indicate that body weight supported training does improve stepping in spinal cord injured humans, and that body weight supported training is superior to conventional rehabilitation (3, 18, 21, 25, 26, 27, 31, 56, 57). Among the many reported positive effects of body weight supported training is an improved ability to step at faster treadmill speeds and an increased weight-bearing ability in the legs. Moreover, evidence indicates that body weight supported training can improve overground walking ability (4, 28, 57). Wernig et al. reported that 80% of acute and chronic spinal cord injured patients (n=87) progressed from wheelchair-bound to independent overground walking after receiving several weeks of body weight supported treadmill training (56). Further, these beneficial effects lasted up to 6 years after the completion of training (57).
The lumbar spinal cord can learn to stand and step in the absence of supraspinal input (2, 6, 9, 12, 14, 15, 22, 23, 24, 37, 41, 42, 45). The capacity of the spinal cord to learn, if appropriately trained, is an extremely important finding for tens of thousands of spinal cord injured patients, as it could mean the difference between being confined to a wheelchair or standing and taking steps. Understanding how to teach the spinal cord to step by providing effective training has immediate clinical application in itself. Moreover, effective body weight supported training can play a role in enhancing the efficacy of other potential therapeutic interventions for spinal cord injuries, such as cell growth, cell engineering and pharmacological treatments (16, 38, 44, 47, 60), by providing an assessment of walking ability following therapeutic intervention.
Locomotor training provides sensory input that is critical for learning to walk Several lines of evidence indicate that the modulation of sensory input from the legs during training plays a significant role in the reorganization of the spinal circuits that generate stepping (9,13, 22, 23, 24, 41, 52). It is generally agreed that load-related information and proprioceptive sensory information are critical variables that must be controlled during locomotor training if stepping ability is to be enhanced. However, optimal procedures for unloading the limbs and assisting limb movements during stepping remain to be determined. In particular, the degree of unloading, the requirement for an alternating gait, and the extent of physical assistance of limb movement are unknown.
It is assumed that partially unloading the limbs is the best approach for training primarily because coordinated stepping movements are difficult to elicit with full weight bearing using current weight support techniques. It is possible that loading the limbs close to or above normal levels may more reliably elicit weight-bearing extension, and, if done repetitively, enhance recovery of stepping. Also, continually adapting weight support levels to adjust loading may provide maximal stimulation of load-related sensory input and therefore, improve stepping. However, current weight support techniques mechanically control weight bearing by adjusting the height of a harness system that suspends the animal or patient. As a consequence, current techniques cannot provide greater than normal loading on the limbs or be rapidly adjusted to adapt to fluctuations in motor output levels.
An alternating walking pattern is typically enforced during locomotor training in spinal cord injured animals and humans. However, it is possible that assisting coordination may not be necessary to recover an alternating pattern. Imposing different patterns of gait during locomotor training can help determine the flexibility of the motor output patterns produced by the spinal cord.
Current training can be characterized as “assist-as-needed” based on the premise that the spinal cord should be allowed to control stepping as much as possible. However, it is possible that simply driving the legs through the appropriate stepping pattern provides the essential sensory input needed to train for this motor task. Alternatively, allowing the spinal cord to freely “explore” the stepping dynamics may be a more effective way for the spinal networks to acquire those dynamics. The generation of error signals appears to be critical for hindlimb withdrawal reflex learning in the spinal cord (30), and a similar phenomenon also may be important in teaching the spinal cord to generate complex motor behaviors such as stepping.
The current method of locomotor training in humans relies on teams of trainers that work as a unit to manually assist leg and trunk movements. Such training is labor-intensive and often imprecise. In cases of flaccid paralysis, trainers must generate and control all leg and trunk movements, acts that can require substantial force, and are called on to repeat these acts hundreds or even thousands of times within one training session of a single person. Manual assistance of the limbs of a small animal during treadmill training is even more difficult to achieve in part because manipulating small limbs cannot be performed in a consistent manner. Robotic systems such as the present invention can bring an unprecedented level of control to spinal locomotion training.
Robotics provides a means to precisely control sensory input during locomotion training. Modern robotic devices can achieve highly dexterous motion, as well as precise quantification of force and motion. These capabilities have made possible a new generation of technology that convincingly simulates and provides control over a wide range of dynamic environments. Dexterous robotic devices are currently being used to enhance neurological rehabilitation (47). Robotic devices for therapy of the hemiparetic arm have been successful in enhancing motor recovery following stroke, and in better assessing that recovery (1, 43, 46).
Treadmill training of human subjects after spinal cord injury also provides an intriguing target for robotic technology (5, 7, 24, 25, 26, 27, 28, 32, 33). Robotic technology could improve experimental control during treadmill training, leading to a better understanding and optimization of training. Robotic technology could also provide a means to quantify in real-time the kinematics and kinetics of stepping. Ultimately, robotics could provide a way to both automate and monitor treadmill training in the clinic, reducing the cost of training and increasing its availability.
Developing robotic devices to provide precise control over body weight supported locomotion training requires an understanding of the engineering and physiological principles of robot-assisted step training. What is needed is a robotic device for test animals that allows experiments to be performed quickly and relatively inexpensively, with a capacity for testing a large number of training strategies. Such a device can enhance basic research of locomotion training and spinal cord learning, provide data on the engineering and physiological principles of robot-assisted step training for application to human therapy, and assess the efficacy of potential therapeutic interventions such as cell growth, cell engineering and pharmacological treatments.
An abstract by Hogan et al. (38) describes a small robot arm apparently used to “apply controlled forces to a rat's forepaw and continuously monitor the kinematics of limb movements”. The rat was described as having a unilateral focal cortical lesion. Apparently, the robot simulated a “linear guide” that would guide the forelimb to a food pellet. However, the robot arm was not applied to the rat's hindlimb, and the robot was not directed to locomotion training.